This disclosure relates to a control device of a sewing machine to execute a sewing operation using a needle thread and a bobbin thread.
Some conventional types of embroidery sewing machines or lockstitch sewing machines are provided with a detection device to detect a remaining amount of bobbin thread wound on a bobbin. In such sewing machines, when a scarcity of remaining amount of bobbin thread wound on the bobbin is detected during an embroidery process, a warning message is displayed as well as forcibly stopping the sewing process. Thus, an execution of a sewing process without the bobbin thread can be prevented.
For example, in Japanese Patent No. 3194432, a sewing machine provided with a bobbin thread remaining amount detection device composed of a reflection type bobbin thread remaining amount sensor is disclosed. This reflection type bobbin thread remaining amount sensor is placed beside a rotary hook positioned below the needle plate having a light emitting element and a light receiving element. The bobbin thread remaining amount detection device detects a bobbin thread remaining amount based on a detection signal outputted from the light receiving element which receives a spot light emitted by the light emitting element when in a needle raised position during a sewing process. When it is detected that a bobbin thread remaining amount has become equal to or less than a predetermined amount by the bobbin thread remaining amount detection device, the sewing machine stops the drive of a sewing machine motor or sets off a warning sound.
Sewing machines have been provided having a bobbin thread remaining amount detection device besides the above, configured by a permeable bobbin thread remaining amount sensor having a light emitting element and a light receiving element arranged to face the rotary hook.
The bobbin is wound with bobbin threads varying in thickness, material and color. Therefore, even in cases when the scarcity of the bobbin thread remaining amount is detected by the bobbin thread remaining amount detection device configured by the reflection type or the permeable type light sensor, it is possible for the bobbin to have approximately 30 cm to 80 cm of bobbin thread remaining, wherein the bobbin thread is wound possibly up to few dozen times. Thus, the bobbin thread remaining amount detection device is not capable of accurately detecting the bobbin thread remaining amount for every thread type.
Furthermore, the conventional sewing machines are configured to immediately stop the drive of the sewing machine motor or set off a warning sound when a remaining amount of the bobbin thread wound on the bobbin has become less than the prescribed amount. Therefore, the remaining approximately 30 cm to 80 cm of bobbin thread is not used and wasted. Also, when a large amount of bobbin thread remains unused, the bobbin needs to be supplied with bobbin thread more frequently, thereby reducing the efficiency of the work.